Water-laid web



United States Patent 3,116,199 WATER-LAID WEB Mamerto M. Cruz, J12,Newtown Square, and Robert L.

McDowell, Springfield, Pa, assignors, by mesne assignments, to FMCCorporation, San Jose, (Jalifi, a corporation of Delaware No Drawing.Filed July 19, 1961, tier. No. 125;}67 14 Qlairns. (till. 162-146) Thisinvention relates to a method of forming Water-laid fibrous productscontaining fibers formed of carboxyalkyl cellulose others.

in the conventional production of water-laid fibrous products such aspapers, naturally occurring cellulose fibers such as wood pulp, cottonlinters and the like are mechanically hydrated as by heating and mixingin a paper mill heater in the presence of a large excess of Water. informing a. pulp slurry as by a beating operaion, the fibers becomehydrated and exhibit a microscopic and sub-microscopic peeling ofindividual fibrils along the surface of the fibers and at the ends ofthe fiber bundles without chemically altering the fiber. The slurry isthen passed to a suitable screen to lay down the fibers as a sheet ormat. The physical properties of the sheet such as strength, tear andburst are dependent to a large extent on an interlocking of the hydratedfibers and or" the fibrillae on the fibers and a fiber-to-fiber bondingwhich develops upon drying. The physical properties of the Water-laidsheets are directly dependent upon the properties of the fibers and thepaper-making process. In general, the natural cellulosic fibers classedas papermaking fibers vary in both diameter and length generally beingfrom about 0.030 mm. to about 0.012 mm. in diameter and from about 0.5to about 4 mm. in length. The fibers are produced by nature and theirphysical properties cannot be altered at will although the propertiesmay be altered Within a given narrow range as by the choice of the rawmaterial, the specific pulping process and the specific paper-makingprocess variables.

Synthetically produced organic fibers offer many functional advantagesin the production of water-laid products because it is possible toaccurately provide fibers of any desired diameter and length mid of anextremely wide range of physical properties. In general, however, thesynthetic organic fibers do not have the fibrillatable structure whichcharacterizes natural cellulose fibers and, accordingly, they do notexhibit natural fiber characteristics when beaten and mixed in a largeexcess of water as in a paper mill beater. ulence, in this sense, theformation 'of water-laid sheets of these synthetic non-fibrillatablefibers per se is unattainable because of intimate interlocking of thefibers can be effected and there is very little, if any, fiber-to-fiberbonding prior to drying or after drying such water-laid sheet. Many ofthe synthetic organic fibers are difficult to disperse in Water and tendto agglomerate so that when they are laid down from a slurry as aWater-laid sheet, they are said to exhibit a very poor sheet formation,particularly Where the fibers are of a length greater than about A inch.In some methods, synthetic fibers are employed in the manufacture ofWaterlaid sheets but it is necessary to employ dispersing agents andadjust the paper-making process variables it uniform sheet formationmust be attained. This is a rather costly operation particularly whendispersing agents are emangles Patented @ec. El, 1963 ployed because alarge portion of the dispersing agent is lost in the white Water.

In order to obtain desired physical characteristics of water-laid sheetsand impart desired characteristics, it is often necessary to utilizecostly high grade paper pulps and incorporate in the sheet various typesof binding or bonding materials. Where the binding materials areincorporated in the fiber slurry, a large portion of the binder is lostin the White Water during sheet formation. Alternatively, the bindingmaterial, where it is water-soluble or water-dispersible, may beincorporated in the wet or dry sheet by im regnation. impregnation,however, requires additional operational procedures and equipment. Asfurther alternatives, the binding or bonding agent may be in the form ofa powdenlike material which is dusted on the sheet, or thermoplasticfibers may be incorporated in the sheet. Where thermoplastic binding orbonding agents are utilized, it is necessary to su cct the sheet at somestage in its manufacture to a heating and pressing operation to activatethe In general, the incorpo ration of binding materials or agentsparticularly geltype binding materials reduces the porosity ofwater-laid products and thermoplastic-type binding or bonding agentsimpart certain stillness and harshness which for many purposes isundesirable.

In the copending application of Battista, Cruz and Reichel, Serial No.67,019, filed November 3, 1968, there is disclosed and claimedwater-laid fibrous sheets and methods of forming such sheets byutilizing a synthetic, homogeneous, hydrophilic fibrous binder havingpredetermined physical characteristics and bonding power. This type offibrous binder is formed of water-insoluble, alkfli-scluble celluloseothers having a degree of substitution of from at least about 0.10 toabout 0.60, one group or" which is Water-insoluble, alkali-solublecarboxyalltyl cellulose others. In accordance with the disclosure ofthis copending application, the water-laid fibrous sheet is formed byincorporating in a fiber slurry the fibrous binders Without any otheralteration in the conventional methods employed in normal paper-makingoperations. The products consist entire y of the fibers constituting thefibrous binder or the products may include other natural or syntheticfibers or mixtures of the various classes of fibers.

One of the purposes of the present invention is to provide a method offorming Water-laid fibrous sheets comprising fibers formed ofcarboxyalliyl cellulose others as hereinbefore described whereby thesheets have improved physical properties.

Other objects and advantages of the present invention will becomeapparent from the description and claims which follow.

The present invention is based ipon our discovery that water-laidcomprising synthetic, homogenellfil'OllS shee s ous, hydrophilic fibrousbinders formed of water-insoluble, alkali-soluble carboxyalhyl celluloseothers having a degree of substitution of from at least about 0.19 toabout 0.6% have enhanced physical properties when the Waterlaid productsare formed from a fiber slurry having a pH above substantially neutralpH to about pl-l 10.5.

As pointed out in the above-identified copending application, it hasbeen proposed to utilize chemicall altered natural cellulose fibers informing water-laid Webs. in

many respects, only the surfaces of such fibers are altered chemicallyand the composition of the fibers is therefore not homogeneousthroughout the fiber. This type of fiber may replace some of the bindingor bonding agents which are frequently employed in increasing the drystrength of water-laid fibrous sheets. Where the waterlaid fibrous sheetis formed entirely of the chemically altered natural cellulose fibers,sues as etherified natural fibers, the optimum physical properties ofthe water-laid sheets are obtained when the etherified fibers have adegree of substitution of about The physical properties of the sheetlevel-oil or decrease from the optimum va ues as the degree ofsubstitution increases above this figure. in this prior art practice, itwas essential that the ether form-ed on and with the cellulose of thefiber be a hydroxyallryl ether.

As disclosed in the copending application, the strength characteristicsof water-laid fibrous sheets formed from the synthetic, homogeneous,hydrophilic binder fibers increase with an increase in the degree ofsubstitution of the cellulose ethers from which the binder fibers areformed and the strength characteristics of water-laid sheets formed inaccordance with the present invention follow the same general pattern.

The present method is applicable only to the fibrous binders which aresynthetically formed from a carboxyalkyl ether of cellulose such ascarboxymethyl cellulose, carboxyethyl cellulose, carboxypropyl celluloseand the like. The homogeneous, fibrous binders are formed syntheticallyfrom an alkali solution of a water-insoluble, alkali-solublecarboxyalkyl ether of cellulose having a degree of substitution of atleast about 0.10 to about 0.60 preferably between about 0.30 and about0.50. The degree of substitution, commonly designated as D.S., is thenumber of substituent groups per anhydroglucose unit of cellulose. Forthe purposes of the present invention, it has been discovered that whenthe [3.8. is below about 0.10, the synthetically produced binder fibersdo not have a sufficient hydrophilic bonding action to appreciablyaffect the properties of the water'laid sheets. On the other hand, wherethe D8. exceeds about 0.60, the fibers when mixed in water tend to losetheir fiber characteristics.

The carboxyalkyl ether of cellulose may be formed by any desired method.Examples of methods for the preparation of this class of cellulose etheras disclosed in U.S. Patents 2,511,060 and 2,577,844. An alkali solutionof the ether is extruded through a spinneret into a conventionalcoagulating and spinning bath such as an aqueous solution of sulfuricacid and sodium sulfate to form filaments of predetermined diameterwhich are then cut to any desired length. As is well known, the diameterand lengths may be varied at will and the strength characteristics ofthe filaments and fibers may likewise be varied within limits by theselection of a specific cellulose ether, by the degree of substitutionof the ether and by the spinning conditions. The properties andcharacteristics of the synthetic fibers may be accurately andreproducibly predetermined. These variations and modifications are wellknown to those skilled in the art and, since they form no part of thepresent invention, no detailed discussion is included herein. The lengthof the fibers for the purposes of the present invention may be fromabout inch to 2 and 3 inches or any other desired length. Normalpaper-making methods generally employ fibers of not more than /4 inch.However, this length is based largely upon historical developmentbecause paper-making fibers are generally of a length of not more thanabout inch.

The synthetic, homogeneous, hydrophilic binder fibers formed of thecarboxyalkyl cellulose ethers differ in many respects from chemicallyaltered natural fibers in that they will be homogeneous in chemicalcomposition, uniform in physical properties, uniform in diameter and uniform in length for any particular application whereas chemically alterednatural cellulose fibers will vary in composition, properties, diameterand length. Advantageously, the carboxyalkyl cellulose ether binderfibers are preferably, but not necessarily, employed in the wet gelstate, that is, in a never-dried condition, and when added to the fiberslurry or to the water, they are in a swollen or highly swollencondition. The synthetic, fibrous binders do not become fibrillated asdo natural paper-making fibers so that when they are to be mixed orblended with natural paper-making fibers, they may be added in theheater after the natural fibers have been beaten, the beater thenserving solely as a mixer. When these synthetic binder fibers areblended with other nonfibrillatable fibers, all of the fibers may beblended in the beater, the beater serving solely as a mixer.

The degree of swelling and the gelatinous condition of the particularcarboxyalkyl cellulose ether fibrous binder will be dependent largelyupon the degree of substitution of the cellulose other from which thefibers were formed. For example, undried synthetic fibers formed of acarboxyet'nyl cellulose having a BS. of about 0.135 are in a swollenstate; synthetic fibers formed of a like ether having a D.S. of about0.3 are in a highly swollen, semigelatinous state; and synthetic fibersformed of a like ether having a D8. of about 0.5 are in a very highlyswollen, almost gelatinous state.

The synthetic binder fibers are readily dispersed in water and appear toaid in dispersing other fibers, both natural and other forms ofsynthetic fibers, in preparing the fiber slurry and are highlycompatible with both naturally occurring fibers and with other syntheticfibers. Because of the swollen or almost gelatinous condition and theirready dispersibility, their presence results in an exceedingly uniformsheet formation when sheeted either by themselves or when mixed orblended with other fibers.

Upon drying the water-laid fiber sheets comprisingor containing thecarboxyalkyl cellulose ether fibrous binder, a high degree offiber-to-fiber bonding occurs because of the initial swollen andsomewhat gelatinous state of these synthetic fibers. The amount offiber-to-fiber bonding varies directly with the D8. of the carboxyalkylcellulose ethers from which the binder fibers are formed. This propertyor characteristic is readily demonstrated by measuring certain physicalproperties of handsheets formed from such synthetic fibers. Standardpaper laboratory techniques utilizing the Noble and Wood cycle beater toform the fiber slurry and the Noble and Wood sheet-mold to formhandsheets in accordance with the standard TAPPl methods may beemployed.

Handsheets were prepared from fibers produced from carboxyethylcellulose ethers formed in accordance with the method disclosed inPatent No. 2,577,844. Briefly, viscose containing 9% cellulose, 6%caustic soda and 31% carbon disulfide based on the weight of thecellulose and having a sodium chloride salt test of 5 was mixed withacrylonitrile, the amount of acrylonitrile being 2%, 4% and 6% basedupon the weight of the viscose. After each sample was mixed at roomtemperature for one hour, the acrylonitrile-viscose mixtures were heldfor 24 hours at atmospheric pressure and room temperature.

The viscoses were then mixed again for one hour to com-- plete thereaction and to drive off ammonia gas. After deaeration overnight at 18(3., the reacted viscoses were spun into an aqueous spinning bathcontaining 12% sulfuric acid, 5% zinc sulfate and 20% sodium sulfate ata temperature of 50 C. and at a spinning speed of 50 a tow of about 1100denier,

meters per minute to form 980 filaments. From the spinning bath, thefilaments were passed through a cascade, the bath containing about 4%sulfuric acid, 1.3% zinc sulfate and 3% sodium sulfate maintained at C.where they were stretched approximately The filaments were then washedand dried on drums and collected on cones. The filaments thus formed haddiameters of 12 to 13 microns and were cut to inch lengths.

in Table I which follows, it will be noted that the 6 at Marcus Hook,Pennsylvania had a pH of about 7.5. in the course or" a year, the pH ofthe tap water varies between about 6.5 and about 7.5 and, for thepurposes of this invention, this range is considered as a substan-(carboxyethyl cellulose, about a D8. of 0.063) had been 5 tially neutralpH.

Table II Ream Breaking Tear Burst Elonga- Caliper Specific Sample pIIAgent Weight Length Factor Factor tion (mils) Vol.

(lbs) (meters) (percent) 4. 4 44. 3 2, e29 201 20 3.1 6.3 2. s 4. e 44.a 2, 550 234 17 2. s 7. 2 2. 7. 43. 9 2, 015 2s? 21 2.1 7. s 1 s. 2 42.a 3, 546 101 30 3. 5 5. s 2. 4 8.7 43.4 3,626 88 30 3.6 5.7 2.4

added, formed sheets which could be tested but such it is quite apparentfrom this table that the strength sheets do not have satisfactorystrength characteristics. On the other hand, Sample C fibers formed fromthe viscose to which had been added 6% acrylonitrile formed satisfactoryhandsheets. It will be noted that this modified viscose formedcarboxyethyl cellulose having a degree of substitution of approximately0.135 which is somewhat above the lower limit of a satisfactory degreeof substitution for the purposes of this invention. The data as notedabove also indicates that as the DS. increases, the dry bonding powerincreases. The ream weight is the calculated weight for 500 sheets each25 inches by 40 inches. The tensile strength is expressed as breakinglength in meters (based on a mm. strip) and is calculated using theformula 47,400X p Ream weight in lbs.

21,500X p Ream weight in lbs.

where p is the breaking load of a 15 mm. strip in kilograms or where Pis the breaking load of a 15 mm. strip in pounds. The

characteristics particularly as measured by the breaking length and bythe burst factor are substantially improved as the pH is increased abovea substantially neutral pH. Although this example merely illustrates theeffect of the pH of the furnish on handsheets formed of carboxyethylcellulose fibers having a D8. of 0.135, like improvements are obtainedwith other carboxyalkyl cellulose ethers within the D.S. range as setforth hereinbefore.

The improvements are not limited to water-laid webs formed entirely ofthe carboxyalkyl cellulose ether fibers. This group of fibers may beutilized as fibrous binders in combination with other fibers, bothsynthetic and natural fibers. In such blends of fibers, the dry bondingpower of the carboxyalkyl cellulose fibrous binders also varies with theincrease in the pH of the slurry or furnish above a substantiallyneutral pH and with the degree of substitution of the carboxyalkylcellulose ether.

It is well known that water-laid sheets, such as handsheets prepared inaccordance with standard TAPPI procedures and formed entirely of viscoserayon filaments have no measurable strength characteristics. Byincorporating fibrous binders formed of carboxyalkyl cellulose ethers,water-laid products may be formed having strength characteristics whichwill be dependent directly upon the proportion of the fibrous binder inthe blend of fibers.

Table 1 P t Ream Breaking Tear Burst Percent Caliper Specific Sample ACND.S W t., lbs. Length Factor Factor Elonga- (mils) Vol.

(meters) tion 2 Too weak to test 4 e. 063 42. 9 1,142 144 8 1. 2 8. 6 3.62 6 0.135 42. 0 2, 327 296 18 1. 9 6. 6 2. 84

Percent ACN-pcrcent aerylonitrile added to the Viscose.

Handsheets cannot be prepared by standard TAPPI methods from allcarboxyalltyl cellulose fibers wherein the ether has a 13.8. at or closeto the upper portion of the range because the sheeted fibers oncollection are so highly swollen and gelatinous in nature that theybecome extruded through the screen upon application of pressure.

The effect of the pH of the slurry or furnish upon the physicalcharacteristics of water-laid webs containing the carboxyalkyl cellulosefibrous binders is readily demonstrated by the measurement of thestrength characteristics of handsheets prepared from fibers formed fromcarboxyethyl cellulose fibers of the type described herenbefore.Carboxyethyl cellulose fibers having diameters of 12 to 13 microns andformed from viscose to which had been added 6% acrylonitrile wereprepared as described in connection with Table l. The cellulose etherhad a D8. of approximately 0.135. Handsheets were formed from slur- -ieswhose pH values were adjusted by the use of various agents and thehandsheets then subjected to conventional physical test methods. Theresults of these tests are presented in Table ll. No adjustment of thepH of the slurry was made in the case of Sample F, the water beingordinary tap water which at the time of the tests Similarly, for anyspecific proportion of fibrous binder, the strength characteristics ofthe products of the fiber blends will vary directly with an increase inthe pH above substantially neutral pH of the fiber slurry or furnish,and with the degree of substitution of the cellulose ether. The strengthcharacteristics relative to the pH will vary as illustrated in Table H.

in Table Ill which follows, there is illustrated the increase inphysical properties with an increase in the proportion of carboxyalkylether fibers. Handsheets were formed from viscose rayon fibers(designated as Fiber R) and from blends of viscose rayon fibers (FiberR) and carboxyethyl cellulose fibers (designated as Fiber X) having a13.8. of 0.135 as described hereinbefore. The rayon fibers were of ahigh tenacity, textile grade viscose rayon having a relatively thickskin and relatively smooth surfaces. All of the fibers had diameters of12 to 13 microns and were cut to inch lengths. The handsheets wereprepared in accordance with standard TAPPI procedures and were subjectedto the standard physical testing procedures as described. The slurriesfrom which the handsheets were formed were prepared with tap waterhaving a pH of about 7.5. As the pH of the slurries is increased, theimprovements in strength characteristics increase as illustrated inTable II.

boxyalkyl cellulose ether fibrous binders with viscose rayon or withnatural paper-making fibers, the improve- Like results are obtained withother types of rayon fibers and other synthetic organic fibers. Thespecific physical characteristics will vary because of variations in thephysical characteristics and properties of the different specific formsof viscose rayon or other synthetic fibers. For example, when lowtenacity, thin skinned viscose rayon fibers are substituted for the hightenacity rayon fibers, the physical properties of the blends of fiberswill, of course, be lower than those set forth in the table.

Like results are also obtained when the carboxyalkyl cellulose etherfibers are blended with natural paper-making fibers. The physicalstrength characteristics of the fibrous products will vary directly withthe proportion of the carboxyalkyl cellulose ether binder fibers, withthe degree of substitution of the cellulose other from which the binderfibers are formed and will also vary directly as the pH is increasedabove substantially neutral pH. The specific strength characteristicswill, of course, be dependent upon the specific natural paper-makingfibers employed in the blends and the relative proportions of thecellulose other fibers and paper-making fibers.

As pointed out in the above-identified copending application, syntheticfibers, such as, for example, rayon fibers, are difficult to disperse inwater because they tend to agglomerate. Various dispersing agents may beincomerated in a slurry to aid in their dispersion and the fibers thendeposited on a screen to form a fairly uniform sheet. The fibrousbinders formed of the carboxyalkyl cellulose others may replace thedispersing agents and they aid in dispersing rayon and other syntheticfibers. Wet waterlaid sheets formed of all viscose rayon fibers of theconventional textile types require special handling to permit theirremoval from a collecting screen. If such sheets are first dried andthen removed from the screen, the sheets have no measurable tensilestrength, tear factor and burst factor. Fibrous binders formed of thecar boxyalkyl cellulose others, when incorporated in the slurry withrayon fibers in an amount as low as 1% by Weight of the rayon fibers,provide Wet water-laid sheets having suificient strength to permit readyremoval from a collecting screen and the dried sheets so formed havemeasurable strength characteristics and the strength characteristics maybe enhanced by sheeting the fiber mixture from a furnish having thecontemplated higher pI-ls.

Many different embodiments of the invention will be apparent and obviousto those skilled in the art and may be made Without departing from thespirit and scope of the invention. It is to be understood that theforegoing specific embodiments are included merely as illustrative andare not intended as limitations.- For example, in the foregoingdiscussion and in the specific examples, the fibers employed haddiameters of from 12 to 13 microns and were cut to inch lengths. Thesedimensions were selected merely as a matter of convenience. As pointedout hercinbe-fore, the fibrous binder may be of any desired length andany desired diameter. Likewise, the products may be of any desiredthickness and may vary from soft, porous, non-woven Webs to harsh,relatively non-porous, parchment-like webs, the latter being formed ofsubstantially all carboxyalkyl cellulose ether fibers having degrees ofsubstitution in the upper portion of the stated range. Although specificreference is made to blends of the carmerit in strength characteristicsare also obtained when the fibrous binders are blended with othersynthetic fibers and other natural fibers or mixtures of synthetic andnatural fibers and the water-laid products are laid down from slurriesor furnishes having pHs Within the stated range.

We claim:

1. In a method of producing water-laid, fibrous products fromdispersions containing synthetic, homogeneous, hydrophilic fibrousbinders formed of a water-insoluble, alkali-soluble carboxyalkylcellulose ether having a degree of substitution of from about 0.10 toabout 9.60, the step of sheeting the fibers of the dispersion to form awaterlaid fibrous product from a dispersion having a pH abovesubstantially neutral pH but not exceeding about pH 10.5.

2. The step in the method as defined in claim 1 wherein thecarbo-xyalkyl cellulose other is carboxymethyl cellulose ether.

3. The step in the method as defined in claim 1 Wherein the carboxyalkylcellulose other is carboxyethyl cellulose ether.

4. The step in the method as defined in claim 1 Wherein the carboxyalkylcellulose ether is carboxypropyl cellulose ether.

5. In a method of producing Water-laid fibrous prod- ,ucts, the stepswhich comprise forming a dispersion of fibers in an aqueous mediumhaving a pH above substantially neutral pH but not exceeding about pH 10.5, at least 1% by Weight of the dispersed fibers being formed of aWater-insoluble, alkali-soluble carboxyalkyl cellulose ether having adegree of substitution of from about 0.10 to about 0.66, sheeting thefibers to form a fibrous prod net and drying the product.

6. The steps in a method as defined in cla'un 5 wherein the carboxyalkylcellulose other is carboxymethyl cellulose ether.

7. The stcps in a method as defined in claim 5 Where- 1 in thecarboxy-al'kyl cellulose other is carboxyethyl cellulose ether.

-8. The steps in a method as defined in claim 5 Wherein the carboxyalkylcellulose other is carboxypropyl cellulose ether.

9. In a method of producing Water-laid fibrous products, the steps whichcomprise f rming a dispersion of fibers in an aqueous medium having asubstantially neutral pH, at least 1% by weight of the dispersed fibersbeing formed of a Water-insoluble, alkali-soluble carboxyl celluloseether having a degree of substitution of from about 0.10 to about 6.60,adjusting the pH of the aqueous medium to a pH above substantiallyneutral pH but not exceeding about pH 10.5, sheeting the fibers to forma fibrous product and drying the product.

it). the steps in a method as defined in claim 9 Wherein thecarboxyalkyl cellulose other is carboxymethyl cellulose ether.

11. The steps in a method as defined in claim 9 Wherein the carboxyalkylcellulose ether is carboxyethyl cellulose ether.

12. The steps in a method as defined in claim 9 Wherein the carboxyalkylcellulose other is carboxypropyl cellulose ether.

5. handsheets prepared from the viscose to which 2% acrylonitrile hadbeen added (carboxyethyl cellulose, about a D8. of 0.02) were too weakfor test purposes. Sample 13 formed from the viscose to which 4%acrylonitrile at Marcus Hook, Pennsylvania had a pH of about 7.5. In thecourse of a year, the pH of the tap water varies etween about 6.5 andabout 7.5 and, for the purposes of this invention, this range isconsidered as a substan- (carboxyethyl cellulose, about a D8. of 0.063)had been 5 tially neutral pH.

Table II Ream Breaking Tear Burst Elonga- Caliper Specific Sample pHAgent Weight Length Factor Factor tion (mils) Vol.

(lbs) (meters) (percent) added, formed sheets which could be tested 'butsuch sheets do not have satisfactory strength characteristics. On theother hand, Sample C fibers stormed from the viscose to which had beenadded 6% acrylonitrile formed satisfactory handsheets. It will be notedthat this modified viscose formed carboxyethyl cellulose having a degreeof substitution of approximately 0.135 which is somewhat above the lowerlimit of a satisfactory degree of substitution for the purposes of thisinvention. The data as noted above also indicates that as the 13.5. increases, the dry bonding power increases. The ream weight is thecalculated weight for 500 sheets each 25 inches by 40 inches. Thetensile strength is expressed as breaking length in meters (based on a15 strip) and is calculated using the formula 47,400X p Ream weight inlbs.

21,5COXp Ream Weight in lbs.

where p is the breaking load of a 15 mm. strip in kilograms or where Pis the breaking load of a 15 mm. strip in pounds. The

urements to the TAPPI standard ream weight.

It is quite apparent from this table that the strength characteristicsparticularly as measured by the breaking length and by the burst factorare substantially improved as the pH is increased above a substantiallyneutral pH. Although this example merely illustrates the effect of thepH of the furnish on handsheets formed of carboxyethyl cellulose fibershaving a D8. of 0.135, like improvements are obtained with othercarboxyalkyl cellulose ethers within the D5. range as set forthhereinbefore.

The improvements are not limited to water-laid Webs formed entirely ofthe carboxyalkyl cellulose ether fibers. This group of fibers may beutilized as fibrous binders in combination with other fibers, bothsynthetic and natural fibers. In such blends of fibers, the dry bondingpower of the carboxyalkyl cellulose fibrous binders also varies with theincrease in the pH of the slurry or furnish above a substantiallyneutral pH and with the degree of substitution of the carboxyalkylcellulose ether.

It is well known that water-laid sheets, such as handsheets prepared inaccordance with standard T APPI procedures and formed entirely ofviscose rayon filaments have no measurable strength characteristics. Byincorporating fibrous binders formed of carboxyalkyl cellulose ethers,water-laid products may be formed having strength characteristics whichwill be dependent directly upon the proportion of the fibrous binder inthe blend of fibers.

Percent ACNperccnt acrylonitrile added to the viscose.

Handsheets cannot be prepared by standard TAPPI methods from allcarboxyalkyl cellulose fibers wherein the ether has a US. at or close tothe upper portion of the range because the sheeted fibers on collectionare so highly swollen and gelatinous in nature that they become extrudedthrough the screen upon application of pressure.

he effect of tie pH of the slurry or furnish upon the physicalcharacteristics of water-laid webs containing the carboxyalkyl cellulosefibrous binders is readily demonstrated by the measurement of thestrength characteristics of handsheets prepared from fibers formed fromcarboxyethyl cellulose fibers or" the type described herenbefore.'Carboxyethyl cellulose fibers having diameters of 12 to 13 microns andformed from viscose to which had been added 6% acrylonitrile wereprepared as described in connection with Table l. The cellulose etherhad a D5. of approximately 0.135. Handsheets were formed from slurrieswhose pH values were adjusted by the use or" various agents and thehandsheets then subjected to conventional physical test methods. Theresults of these tests are presented in Table ll. No adjustment of thepH of the slurry was made in the case of Sample F, the water beingordinary tap water which at the time of the tests Similarly, for anyspecific proportion of fibrous hinder, the strength characteristics ofthe products of the fiber blends will vary directly with an increase inthe pH above substantially neutral pH of the fiber slurry or furnish,and with the degree of substitution of the cellulose ether. The strengthcharacteristics relative to the pH will vary as illustrated in Table ll.

in Table Ill which follows, there is illustrated the increase inphysical properties with an increase in the proportion of carooxyalkylether fibers. Handsheets were formed from viscose rayon fibers(designated as Fiber R) and from blends of viscose rayon fibers (FiberR) and carboxyethyl cellulose fibers (designated as Fiber X) having aD8. of 0.135 as described hereinbefore. The rayon fibers were of a hightenacity, textile grade viscose rayon having a relatively thick skin andrelatively smooth surfaces. All of the fibers had diameters of 12 to 13microns and were cut to A. inch lengths. The handsheets were prepared inaccordance with standard TAPPI proce dures and were subjected to thestandard physical testing procedures as described. The slurries fromwhich the handsheets were formed were prepared with tap water having apH of about 7.5 As the pH of the slurries is increased, theimprovements. in strength characteristics increase as illustrated inTable ll.

3 8 boxyalkyl cellulose ether fibrous binders with viscose rayon or withnatural paper-making fibers, the improve- Like results are obtained withother types of rayon fibers and other synthetic organic fibers. Thespecific physical characteristics will vary because of variations in thephysical characteristics and properties of the different specific formsof viscose rayon or other synthetic fibers- For example, when lowtenacity, thin skinned viscose; rayon fibers are substituted for thehigh tenacity rayon fibers, the physical properties of the blends offibers will, of course, be lower than those set forth in the table.

Like results are also obtained when the oarboxyalkyl cellulose etherfibers are blended with natural paper-male ing fibers. The physicalstrength characteristics of the fibrous products will vary directly withthe proportion of the carboxyal kyl cellulose ether binder fibers, withthe degree of substitution of the cellulose ether from which the binderfibers are formed and will also vary directly as the pH is increasedabove substantially neutral pH. The specific strength characteristicswill, of course, be dependent upon the specific natural paper-makingfibers employed in the blends and the relative proportions of thecellulose ether fibers and paper-making fibers.

As pointed out in the above-identified copending application, syntheticfibers, such as, for example, nayon fibers, are difficult to disperse inwater because they tend to agglomerate. Various dispersing agents may beincorporated in a slurry to aid in their dispersion and the fibers.

then deposited on a screen to form a fairly uniform sheet.

The fibrous binders formed of the carboxyalkyl cellulose others mayreplace the dispersing agents and they aid in dispersing rayon and othersynthetic fibers. Wet water-- laid sheets formed of all viscose rayonfibers of the conventional textile types require special handling topermit: their removal from a collecting screen. If such sheets are firstdried and then removed from the screen, the

sheets have no measurable tensile strength, tear factor" and burstfactor. Fibrous binders formed of the car-- boxyalkyl cellulose others,when incorporated in the slurry with rayon fibers in an amount as 'lowas 1% by weight of the rayon fibers, provide wet water-laid sheetshaving sufiicient strength to permit ready removal from a collectingscreen and the dried sheets so formed have measurable strengthcharacteristics and the strength characten istics may be enhanced bysheeting the fiber mixture from a furnish having the contemplated higherpHs.

Many different embodiments of the invention will be apparent and obviousto those skilled in the art and may be made without departing from thespirit and scope of the invention. It is to be understood that theforegoing specific embodiments are included merely as illustrative andare not intended as limitations. For example, in the foregoingdiscussion and in the specific examples, the fibers employed haddiameters of from 12 to 13 microns and were cut to inch lengths. Thesedimensions Were selected merely as a matter of convenience. As pointedout hereinbefore, the fibrous binder may be of any desired length andany desired diameter. Likewise, the products may be of any desiredthickness and may vary from soft, porous, non-woven webs to harsh,relatively nonporous, parchment-like webs, the latter being formed ofsubstantially all carboxyalkyl cellulose ether fibers having degrees ofsubstitution in the upper portion of the stated range. Although specificreference is made to blends of the carment in strength characteristicsare also obtained when the fibrous binders are blended with othersynthetic fibers and other natural fibers or mixtures of synthetic and 7natural fibers and the water-laid products are laid down from slurriesor furnishes having pHs within the stated range.

We claim:

1. in a method of producing water-laid, fibrous products fromdispersions containing synthetic, homogeneous, hydrophilic fibrousbinders formed of a water-insoluble, alkalieoluble carboxyalkylcellulose ether having a degree of substitution of from about 0.10 toabout 0.60, the step of sheeting the fibers of the dispersion to form awaterlaid fibrous product from a dispersion having a pH abovesubstantially neutral pH but not exceeding about pH 16.5.

2. The step in the method as defined in claim 1 where- :in thecarboxyalkyl cellulose ether is carboxymethyl cellulose ether.

3. The step in the method as defined in claim 1 wherein thecarboxyal'kyl cellulose ether is carboxyethyl cellulose ether.

4. The step in the method as defined in claim. 1 Wherein thecarboxyalkyl cellulose ether is carboxypropyl cellulose ether.

5. In a method of producing water-laid fibrous products, the steps whichcomprise forming a dispersion of fibers in an aqueous medium having a pHabove substantially neutral pH but not exceeding about pH 10.5, at least1% by weight of the dispersed fibers being formed of a water-insoluble,alkali-soluble carboxyalkyl cellulose ether having a degree ofsubstitution of from about 0.10 to about 0.60, sheeting the fibers toform a fibrous prodnot and drying the product.

6. The steps in a method as defined in claim 5 wherein the carboxyalkylcellulose ether is carboxymethyl cellulose ether.

7. The steps in a method as defined. in claim 5 wherein the carboxyalkylcellulose ether is oarboxyethyl cellulose ether.

8. The steps in a method as defined in claim 5 wherein the carboxyalkylcellulose ether is carboxypropyl cellulose ether.

9. in a method of producing water-laid fibrous products, the steps whichcomprise forming a dispersion of fibers in an aqueous medium having asubstantially neutral pH, at least 1% by weight of the dispersed fibersbeing formed of a water-insoluble, alkali-soluble carboxyl celluloseether having a degree of substitution of from about 0.10 to about 0.60,adjusting the pH of the aqueous medium to a pH above substantiallyneutral pH but not exceeding about pH 10.5, sheeting the fibers to forma fibrous product and drying the product.

10. 'lhe steps in a method as defined in claim 9 wherein thecarboxyalkyl cellulose other is carboxymethyl cellulose ether.

ll. he steps in a method as defined in claim 9 wherein the carboxyalkylcellulose ether is carboxyethyl cellulose ether.

12. The steps in a method as defined in claim 9 wherein thecarboxyallryl cellulose other is carboxypropyl cellulose ether.

13. In a method of producing Water-laid fibrous products, the stepswhich comprise forming a dispersion of fibers in an aqueous mediumhaving a substantially neutral pH, at least 1% by Weight of thedispersed fibers being formed of a water-insoluble, alkali-solublecarboxyalkyl cellulose ether having a degree of substitution of fromabout 0.10 to about 0.60, the balance of the fibers being viscose rayonfibers, adjusting the pH of the aqueous medium to a pH abovesubstantially neutral pH but not exceeding about pH 10.5, sheeting thefibers to form a fibrous product and drying the product.

14. In a method of producing water-laid fibrous products, the stepswhich comprise forming a dispersion of fibers in an aqueous mediumhaving a substantially neutral pH, at least 1% by Weight of thedispersed fibers being formed of a Water-insoluble, alkali-solublecarboxyalkyl cellulose ether having a degree of substitution of fromabout 0.10 to about 0.60, the balance of the fibers being naturalpaper-making fibers, adjusting the pH of the aqueous medium to a pHabove substantially neutral pH but not exceeding about pH 10.5, sheetingthe fibers to form a fibrous product and drying the product.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN A METHOD OF PRODUCING WATER-LAID, FIBROUS PRODUCTS FROM DISPERSINSCONTAINING SYNTHETIC, HOMOGENEOUS, HYDROPHILIC FIBROUS BINDERS FORMED OFA WATER-INSOLUBLE, ALKALI-SOLUBLE CARBOXYALKYL CELLULOSE ETHER HAVING ADEGREE OF SUBSTITUTION OF FROM ABOUT 0.10 TO ABOUT 0.60, THE STEP OFSHEETING THE FIBERS OF THE DISPERSION TO FORM A WATERLAID FIBROUSPRODUCT FROM A DISPERSIN HAVING A PH ABOVE SUBSTANTIALLY NEUTRAL PH BUTNOT EXCEEDING ABOUT PH 10.5.